The present invention relates to a cutting edge well suited for use in the blade of a construction machine or track particularly used for snow removal.
Snow removal conventionally carried out by a motor grader or the like involves operation for removing snow cover and sherbet-like snow and operation for scraping snow which has been compressed into a frozen path (hereinafter called xe2x80x9ccompressed snowxe2x80x9d). Snowremoving cars usually travel at a speed of about 30 km/h for removing snow cover and sherbet-like snow, and in the event of collision with projecting obstacles such as a manhole lid or a joint of a bridge during snow cover removal, a big shock occurs at the cutting edge end of the blade and causes chipping or cracking unless the cutting edge of the blade is made of a material having high toughness. For easy compressed snow removal, snowremoving cars travel with the blade being tilted (to change the angle of the blade edge), thereby grinding the tip of the cutting edge to be sharpened. However, in cases where the material of the blade cutting edge is low in toughness, the cutting edge would be chipped when its angle is changed with its tip portion in a sharpened condition.
For solving the chipping problem of blade cutting edges, there have been proposed, up to now, various means for increasing the durability of a blade cutting edge. Examples of them are as follows.
(1) The most popular one is the cutting edge such as disclosed in Japanese Patent Publication (KOKAI) Gazette No. 9-158144 (1997), which is made from steel for machine construction use (e.g., SCM435) which underwent thermal treatment to have a hardness of HRC 45 to 55. The cutting edge 100 disclosed in this publication is designed as shown in FIG. 21. Specifically, the tip portion 102 of an edge member 101 made from a steel plate of a specified size is sharpened and partially cut to form indents 103 at a specified pitch, thereby forming ground contacting teeth 104 at spaced intervals in the form of saw teeth. Reference numeral 105 is a mounting hole.
(2) The cutting edge 106 disclosed in Japanese Patent Publication (KOKAI) Gazette No. 8-302757 (1996) is designed, as shown in FIG. 22, such that a plurality of teeth 108 made from a hard metal (tungsten carbide) are attached to a main body 107 having high impact resistance. More specifically, a stepped portion 109 is formed at the leading end of the surface of the main body 107 and the plurality of divided teeth 108 arranged in a widthwise direction are brazed to the stepped portion 109.
(3) There are known cutting edges which use, in their leading edges, a hard material in which a hard substance such as crushed hard metal grains is dispersed in a low-melting metal, and examples of such cutting edges are as follows.
{circle around (1)} Japanese Utility Model Publication (KOKAI) Gazette No. 55-85155 (see FIG. 23) according to which a hard material 110 is formed by enclosing a core material 111 by a plate 113 made of an appropriate metal (e.g., soft steel), the core material 111 being formed by integral solidification of crushed grains 112 of a hard alloy such as tungsten carbide in a solution of a base metal such as copper alloy.
{circle around (2)} Japanese Patent Publication (KOKAI) Gazette No. 56-13465 (see FIG. 24) according to which a hard material 115 is formed by dispersing crushed hard metal grains 117 in a low-melting alloy 118 within a flat box the three side of which are formed from a metal plate (steel plate) 116 which is easy to weld.
{circle around (3)} Japanese Patent Publication (KOKAI) Gazette No. 53-78602 (see FIG. 25) according to which a cutting edge 120 is formed by inserting a wear resistant plate-like piece 121 (hard material) made from a synthetic material containing wear resistant grains 122 so as to be held between two partially thinned steel plates 123, 123 and then integrated with the latter by welds 124, 124xe2x80x2 (plug welds).
(4) A cutting edge made of a casting in which the leading end of the edge is provided with hard metal grains as an insert (produced by Pacal (U.S.A.)).
(5) The cutting edge such as disclosed in Japanese Patent Publication (KOKOKU) Gazette No. 5-54543 (see FIG. 26). The cutting edge 125 has an edge body 126 and two kinds of hard metals 127, 127xe2x80x2 are brazed to the leading end of the edge body 126 in the form of layers, thereby achieving both wear resistance and impact resistance.
(6) The cutting edge having a bit mounted on its leading end (produced by Kennametal Inc. (USA)).
(7) The cutting edge such as disclosed in PCT Publication WO97/44994 (see FIG. 27). In the cutting edge 130, holes 133 are made at the leading end 132 of an edge body 131 at a specified pitch in a widthwise direction and pins 134 made from a hard metal are inserted into these holes 133 so as to project from the leading end 132 of the edge body 131 by an appropriate length t.
(8) The cutting edge disclosed in Japanese Patent Publication (KOKAI) Gazette No. 11-166249 (see FIG. 28). In the cutting edge 135, a hard material layer 137 is formed on the leading end of an edge body 136 by overlaying of a hard material.
The above known techniques have, however, revealed the following disadvantages. The cutting edge (1) is inexpensive and less dangerous, but has short service life, requiring frequent edge replacement. Service life can be improved by increasing the thickness of the edge, but this disadvantageously increases ground contact area and therefore decreases ground contact pressure, entailed by decreased compressed snow removal performance. With intent to increase compressed snow removal performance, the ground contact teeth 104 are arranged at spaced intervals in the form of comb teeth as shown in FIG. 21. However, increased ground contact pressure causes significant wear, resulting in extremely short life.
The cutting edge (2) shown in FIG. 22 uses teeth 108 made of a hard metal without processing/treatment, so that the cutting edge (2) costs high and has a high risk of breakage due to big cracks if the very brittle hard metal teeth directly collides with projecting obstacles such as rocks.
The following problem is presented by the cutting edges (3) which use a hard material of a structure in which a hard substance such as crushed hard metal grains is dispersed within a low-melting metal. Since wear due to scratching mainly occurs in snow removal, if the hard metal grains (hard grains) are small in size, the supporting base metal part is scooped away and looses its supporting force so that the hard metal grains drop off before they exert their intrinsic wear resistance. As a result, high wear resistance cannot be achieved.
The cutting edge (3)-{circle around (1)} shown in FIG. 23 is formed by cladding the core material 111 with the plate 113 made of soft steel such that the plate 113 encloses the entire periphery of the core material 111 in its longitudinal section, and therefore the hard grains (crushed grains 112) to be contained in the hard material cannot be introduced from other areas than the longitudinal end face. This cutting edge, therefore, suffers from the problem that where the entire length of the hard material is long, large-sized hard grains are difficult to introduce and likely to be nonuniformly dispersed.
The cutting edge of (3)-{circle around (2)} shown in FIG. 24 has the disadvantage that where the hard material is welded to a blade or the like at the retaining back face which is formed by the metal plate (steel plate) 116 and located opposite to the surface in which the hard grains (crushed grains 117) are dispersed, the surface having the hard grains (crushed grains 117) are easily chipped or broken as it is susceptible to impact force due to direct collision with soil and rocks. The cutting edge (3)-{circle around (3)} shown in FIG. 25 is complicated in structure and costly.
The cutting edge (4) has a disadvantage attributable to its manufacturing process which involves internal casting of the edge. Specifically, with this process, the thickness of the edge is increased so that ground contact pressure decreases, causing difficulty in compressed snow removal, and further, poor toughness increases the risk of chipping.
The cutting edge (5) (see FIG. 26) is efficient, enjoying long service life, but its manufacturing cost is very high. In addition, the edge is thick at its leading end, which causes decreased ground contact pressure and therefore difficulty in compressed snow removal.
The cutting edge (6) having a bit mounted on its leading edge is also very expensive. Although this cutting edge effectively works in compressed snow removal but suffers from the problem of remaining snow in snow removal.
The cutting edge (7) shown in FIG. 27 has the same problems as those of the cutting edge (6), and additionally, it has the disadvantage that the hard metal pins 134 easily drop off in service.
The cutting edge (8) shown in FIG. 28 has the hard material layer 137 overlaid on its front face and this hard material layer 137 is easily chipped when tilting the cutting edge during snow removal, so that long service life cannot be expected.
The present invention has been directed to overcoming the foregoing problems and a prime object of the invention is therefore to provide a cutting edge which exhibits excellent wear resistance with respect to friction caused by scratching, this resistance being particularly required for cutting edges for snow removal, which provides increased efficiency in compressed snow removal, and which can be manufactured at comparatively low cost.
The above object can be achieved by a cutting edge according to the invention which comprises an edge body mounted on a blade and a hard member provided at the leading end of the edge body,
wherein the hard member comprises:
a hard material containing hard grains which are dispersed with high filling density and are integrally combined by a metal having a lower melting point than the hard grains; and
a protective member which covers at least the front face of the hard material as viewed in the travel direction of the blade and which has impact resistance.
According to the cutting edge of the invention, since a hard material formed from hard grains dispersed with high filling density and combined by a low-melting metal is mounted with an impact-resistant protective member attached to its front side as viewed in the travel direction of the blade, the protective member (i.e., steel material portion) positioned on the front face of the hard material protects the hard material so that the hard material will not be chipped if impact is exerted thereon. If the blade is tilted, the leading edge of the edge body will be sharpened but will not be chipped because the leading end portion is made from e.g., steel. Since the edge is formed from the hard material protected by the protective member, it has resistance to scratching wear and, in consequence, can be used for a long time.
In the invention, the protective member is preferably constituted by a part of the edge body. With this arrangement, the edge body doubles as the protective member for the hard material and there is no need to form the protective member separately.
In this case, the hard material may be disposed on the back face side of the edge body as viewed in the travel direction of the blade and at least the back face of the hard material as viewed in the travel direction of the blade may be covered with the steel plate. In addition, the edge body may be provided with a groove at its ground contact face and the hard material may be disposed within the groove.
In the invention, the protective member may be distinct from the edge body, formed by bending a steel plate into a substantially L shape and attached to the leading end of the edge body. Alternatively, the protective member may be distinct from the edge body, formed by bending a steel plate so as to cover the three faces of the edge body excluding its ground contact face and attached to the leading end of the edge body.
In the invention, it is preferable that the hard grains be crushed and/or granulated grains of a hard metal mainly containing a tungsten carbide alloy. As the low-melting metal, Cu, a Cu alloy or an Ni self fluxing alloy is preferably used.
In the invention, the hard material preferably contains large diameter hard grains having diameters of 1 mm or more and distributed in the entire area of the hard material. Since the parent phase metal retaining the hard grains is firstly worn, if the hard grains are small in size, the retaining force of the parent phase metal for the hard grains is weakened so that the hard grains easily drop off. On the other hand, if the hard grains are large in size, they are unlikely to drop off because of the strong retaining force of the parent phase metal. In cases where the hard grains have diameters of 1 mm or more, even if the hard grains project from the wear surface by 1 mm, there remains, on the rear side as viewed in the travel direction of the blade, the parent phase metal supporting the hard grains, so that the hard grains are unlikely to drop off. Moreover, the projecting hard grains function to scrape compressed snow. For this reason, it is desirable for cutting edges for snow removal to use large hard grains having diameters of 1 mm or more.
By blending and distributing the large diameter hard grains and small diameter hard grains having diameters of 0.5 mm or less, the filling density of the hard grains can be increased. In addition, filling with large and small diameter hard grains at high density has the effect of increasing resistance to scratching wear and therefore service life, since the gaps between the large diameter hard grains are filled with the small diameter hard grains, thereby reinforcing the hard material.
It is preferable to make the leading end of the hard member such that thick portions and thin portions are alternately arranged in the widthwise direction of the edge body. This makes parts of the leading end thin, thereby increasing ground contact pressure and therefore compressed snow removal performance can be improved. In addition, the combination of the steel portion having impact resistance throughout it and the hard material having high wear resistance prevents chipping and excessive wear, so that durability is increased and improved service life is consequently ensured.
Preferably, the hard materials are spaced at appropriate intervals in the widthwise direction of the edge body at the leading end of the hard member. With this arrangement, the areas where no hard material is provided are preferentially worn, forming slight unevenness at the leading end of the hard member with the areas provided with the hard material becoming convex and having increased ground contact pressure, so that compressed snow removal performance can be improved.
It is also preferable that the hard materials different in wear resistance be alternately arranged in the widthwise direction of the edge body at the leading end of the hard member. Thanks to the difference in wear resistance, the tips of the areas where the hard material having higher wear resistance is disposed slightly project so that the ground contact pressure at the projecting areas increases with improved compressed snow removal performance like the foregoing case and service life is also extended.
Preferably, the hard member is attached to the leading end of the edge body by infiltration of the low-melting metal. This arrangement has the advantage that the hard material containing the hard grains mixed and dispersed therein at high density can be easily manufactured and can be securely mounted on the edge body. Also, the infiltration has such an advantage in manufacture, particularly, in cases where thick portions and thin portions are alternately arranged in the widthwise direction of the edge body to form the leading end of the hard member, that the thickness of the hard member can be easily varied by corrugating the wall portion when constructing the outer shell with the member having impact resistance.
The hard member may be attached to the leading end of the edge body by welding. Alternatively, it may be attached to the leading end of the edge body by brazing. It is also possible to attach the hard member to the leading end of the edge body by bolting. The same effect as described earlier can be attained by any of these means.